While the 300 can decode Dolby True HD internally as far as I know it can not bitstream Dolby True HD. So your Pioneer VSX-91TXH will not say Dolby True HD on the display, I am sure the only thing it will say is multi channel in. You would have to get a player that can bitstream if you want the revciever to do the decoding.
I own the BDP-S300 and while it is a nice player it does not bitstream anything but standard lossy Dolby Digital & DTS. I use the multi channel analog out when listening to Dolby True HD. I believe that if you go into the setup menu/audio and then choose PCM for the audio HDMI. That should send the decoded Dolby True HD as PCM audio via HDMI. Otherwise you can decode it in the player and send it out via multi-channel out on the player. But you will limit yourself to 5.1 via the analog audio outputs, and I believe that you can do 7.1 via HDMI.